Method for treating paperboard



United States Patent" METHOD FOR TREATING PAPERBOARD Sol Chaftan, Bronx, N. Y.

No Drawing. Application November 18, 1952, Serial No. 321,286

3 Claims. (Cl. 117-76) In spite of the tremendous increase in the production of the various types of paper board in the last few decades, there has been only a very limited improvement in the quality of the boards. Thus the cheapest and there-fore the most widely used of these, chipboard, is still a very weak board, tears easily, lacks rigidity unless built up to a considerable thickness, and in case of damage by water practically disintegrates. Kraftboard is a stronger board but costs more and also lacks rigidity and has no water resistance whatever. Juteboard, which is the strongest of all and the costliest, still has limited tear resistance and rigidity and is affected by water.

In order to provide some water resistance and add strength to paperboard, rosin, chemically termed abietic acid which is a product of distillation of coniferous woods and is the amber colored glossy residue left after distilling off the oil of turpentine, has been used by the paper industry for over a century as a size mixed with the pulp in the beater. The action of rosin consists in coating the cellulose fibers of the paper. However, only a limited amount of rosin can be incorporated in the pulp because it does not combine directly with the Wet cellulose fibers, and aluminum sulphate must be used in order to effect the coating of the fibers thereby. The commonly accepted theory behind this action is that cellulose fibers in water carry minute negative charges as do the particles of rosin so that they repel each other. As particles of aluminum are positively charged with a stronger charge, they are attracted to the cellulose fibers which become positively charged and then attract the rosin particles. Since aluminum sulphate has certain undesirable side effects on the finished product and corrodes the paper-making machinery, its use must be limited, thus limiting the quantity of rosin in the pulp.

Prevailing methods of impregnating board after man-w facture have been limited to treatment with wax which has the tendency to weaken the board so that the use of wax has generally been limited to the stronger and more expensive types of board.

It is accordingly the principal objects of this invention to provide a paperboard having fibers which are saturated with rosin to make the board thoroughly Water-resistant throughout, and a method for making the same. I j

Further objects are to provide a paperboard which has marked rigidity and strength, which is fire retardant, which does not require heat or pressure in its manufacture, which is low in cost, and which advances the art generally.

In accordance with my invention to treat paper prod ucts including among others paper and paperboard, such as chipboard, kraftboard, corrugated board, juteboard, to develop the optimum properties of strength, rigidity, and water resistance, I prepare a solution consisting of an organic solvent to which is added rosin to the amount of twenty to thirty parts by weight per hundred parts of solution. The board is immersed in this rosin Patented Apr. 23, 1957 solution for a sufficient time to thoroughly saturate its fibers with rosin, the approximate period required for boards of 10 to 60 mils in thicknesses being two to three seconds.

Paperboard treated as described above will exhibit strength and rigidity within twenty-four hours of the treatment but to stabilize the treated board against changes in atmospheric conditions and further increase its strength and rigidity I immerse the board in a further bath immediately after dipping in the rosin solution. This further bath consists of an organic solvent which is preferable although not necessarily the same as used for the rosin solution in which is dissolved a methyl methacrylate polymer in an amount of ten to twenty parts by weight per hundred parts of solution. After an immersion in the resin solution for several seconds the board is allowed to dry for approximately twentyfour hours after which period the board is water-resistant throughout, its surface is hard and its strength and rigidity are markedly increased as compared with nontreated board as it comes from the mill.

As solvents for the rosin and methyl methacrylate poiymer any suitable organic solvent may be used. I have found solvents of the following classification to be particularly effective:

1. Ketones:

Methyl ethyl ketone Methyl isobutyl ketone Di-isobuty-l ketone Methyl propyl ketone 2. Esters:

Methyl acetate Ethyl acetate 11 Propyl acetate 11 Butyl acetate Isobytul acetate Amyl acetate Heyl acetate 3. Alcohols:

Ethyl alcohol Propyl alcohol lsopropyl alcohol Di-acetone alcohol Butyl alcohol Amyl alcohol Z-ethoxyethanol The following are typical examples of solutions which have been prepared in accordance with my invention:

Example I I dip a dry sheet of chipboard in a first solution of 15 parts of rosin and parts of methyl ethyl ketone by weight for a period of two seconds immediately following which I dip the chipboard sheet in a second solution of 10 parts of methyl methacrylate polymer and parts of methyl ethyl ketone by weight for a period of two seconds following which the sheet is dried at room temperature [for twenty-four hours.

Example II I dip a dry sheet of chipboard in a first solution of 15 parts of rosin and 85 parts of methyl isobutyl ketone by weight for a period of two seconds immediately following which I dip the chipboard sheet in a second solution of 10 parts of methyl methacrylate polymer and 90 parts of methyl isobutyl ketone by weight for a period of two seconds following which the sheet is dried at room temperature for twenty-four hours.

3 Example III I clip a dry sheet of kraftboard in a first solution of 15 parts of rosin and 85 parts of Z-ethoxyethanol by weight for a period of three seconds immediately following which I dip the kraftboard sheet in a second solution of parts of methyl methacrylate polymer and 90 parts of Z-ethoxyethanol by weight for a period of three seconds following which the sheet is dried at room temperature for twenty-four hours.

Example IV I dip a dry sheet of juteboard in a first solution of parts of rosin and 85 parts of 2-ethoxyethanol by weight for a period of three seconds immediately following which I dip the juteboard sheet in a second solution of 10 parts of methyl methacrylate polymer and 90 parts of 2-ethoxyethanol by Weight for a period of three seconds following which the sheet is dried at room temperature for twenty-four hours.

Although I prefer to use two separate baths for impregnating the board with the rosin and resin because of ease of control and a superior resulting product, it is possible to obtain generally satisfactory results by dissolving both the rosin and resin in the same solvent bath. Although I generally prefer dipping because of the economies in time and money, for very large sheets or small runs, it is also possible to carry out the above described process by painting or spraying the various solutions upon the paperboard.

If desired, fire retardant properties can be developed in the board by dipping in a solution made by dissolving in water a penetrating fire retarding salt such as is sold under the Du Pont trade name CM and consisting principally of ammonium sulphanate. After dipping in the salt solution the board is thoroughly dried and the rosin and methyl methacrylate polymer applied as described in detail heretofore. Alternatively a fire retardant such as carbon tetrachloride can be used to replace a portion of the organic solvent.

Example V I dip a sheet of chipboard in a solution of one and one-half (1 /2) pounds of Du Pont CM in each gallon of water until the sheet is thoroughly Wetted. After drying the sheet is dipped in a first solution of 15 parts of rosin and 85 parts of methyl ethyl ketone by Weight for a period of two seconds immediately following which I dip the chipboard sheet in a second solution of 10 parts of methyl methacrylate polymer and 90 parts of methyl ethyl ketone by weight for a period of tWo seconds following which the sheet is dried at room temperature for twenty-four hours.

Example V] I dip a sheet of chipboard in a solution of 15 parts of rosin, 10 parts of methyl methacrylate polymer,

parts carbon tetrachloride, and 55 parts methyl ethyl ketone by weight for two seconds following which the sheet is dried at room temperature for twentyfour hours.

I claim:

1. The method of increasing the strength, rigidity and water-resistance of paper products, comprising applying a rosin solution to said product to saturate the fibers thereof, said rosin solution consisting essentially of rosin dissolved in an organic solvent in an amount to give a solution of ten to thirty parts rosin per hundred parts by weight, applying a methyl methacrylate polymer solution to said product to produce a hard outer coating, said polymer solution consisting essentially of methyl methacrylate polymer resin dissolved in an organic solvent to give a solution of ten to twenty parts resin per hundred parts by weight, and drying the product.

2. The method of increasing the strength, rigidity and water-resistance of paper products, comprising applying a rosin and methyl methacrylate polymer resin solution to said product, said solution consisting essentially of rosin and methyl methacrylate dissolved in an organic solvent, the rosin comprising ten to thirty parts by Weight and the methyl methacrylate polymer resin ten to thirty parts by weight per hundred parts by Weight, and drying the product.

3. The method of increasing the strength, rigidity and Water-resistance of paper products, comprising applying a rosin solution to said product, said rosin solution consisting essentially of rosin dissolved in an organic solvent in an amount to give a solution of ten to thirty parts rosin per hundred parts by Weight, applying a methyl methacrylate polymer solution to said product to produce a hard outer coating, said polymer solution consisting essentially of methyl methacrylate polymer resin dissolved in an organic solvent to give a solution to ten to twenty parts resin per hundred parts by weight, and drying the product.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Gregory: Uses and Applications of Chemicals and Related Materials (1939), page 153.

The Merck Index, 6th ed. (1952).

Condensed Chemical Dictionary, Corp, 1942, page 436.

Reinhold Pub. 

1. THE METHOD OF INCREASING THE STRENGHT RIGIDITY AND WATER-RESISTANCE OF PAPER PRODUCTS, COMPRISING APPLYING A ROSIN SOLUTION TO SAID PRODUCT TO SATURATE THE FIBERS THEREOF, SAID ROSIN SOLUTION CONSISTING ESSENTIALLY OF ROSIN DISSOLVED IN AN ORGANIC SOLVENT IN AN AMOUNT TO GIVE A SOLUTION OF TEN TO THIRTY PARTS ROSIN PER HUNDRED PARTS BY WEIGHT, APPLYING A METHYL METHACRYLATE POLYMER SOLUTION TO SAID PRODUCT TO PRODUCE A HARD OUTER COATING, SAID POLYMER SOLUTION RESIN CONSISTING ESSENTIALLY OF METHYL METHACRYLATE POLYMER RESIN DISSOLVED IN AN ORGANIC SOLVENT TO GIVE A SOLUTION OF TEN TO TWENTY PARTS RESIN PER HUNDRED PARTS BY WEIGHT, AND DRYING THE PRODUCT. 